An examination of predator control techniques for the protection of critically endangered species.

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Abstract

Feral cats (Felis catus) have been shown to be a main contributor to species decline throughout the world and are especially threatening to insular species that lack adequate defense characteristics. Feral cat control programs have been implemented on islands throughout the world with varied success. Many islands present unique limitations and therefore require custom control strategies. Furthermore, the adaptive nature of feral cat populations makes it difficult to predict space use and the effect of control on population size. To mitigate the impact of feral cats on threatened species, space use data are commonly used to design control strategies. With the use of GPS data logging collars, chapter two describes daily space use and home ranges of feral cats that threaten an endangered species on Rota Island in the Commonwealth of the Northern Mariana Islands. Using 100% Minimum Convex Polygon (MCP), average adult male home range was 1.32 km² and average adult female home range was 0.22 km². Home ranges were deemed fully revealed if asymptotes were reached using incremental analysis. A Michaelis-Menten model was applied to predict home ranges of cats with datasets that did not show convergence. The ability of the model to estimate home ranges of cats with limited location datasets was evaluated by comparing predictions derived from truncations of the full time series of complete datasets. Findings suggest that cat management on Rota should be multifaceted in order to maximize the protection of endangered species and that the Michaelis-Menten model is a useful tool for home range analysis. Chapter three examines the Rota hunting strategy to determine its impacts on the population. A discrete form of the Schaefer model was applied to a 29-month time series of control data. A likelihood framework was used to determine maximum likelihood parameter estimates and calculate population projections to compare control strategies. Model results suggest that the hunting strategy on Rota was effective at initially reducing the cat population, however an unfeasible amount of effort would be required to maintain such a rate of decline. Findings show that it is feasible to maintain cat abundance at lower levels and suggest that a concentrated-effort strategy is preferable to a fixed-effort strategy. While more complex population model forms are available, the Schaefer model is well suited for assessing the impacts of limited predator control programs, such as the one conducted on Rota Island.